904 A. B. DAWSON 
C. Mixed glands 
1. In other Amphibia. In the introduction to the discussion 
of the glands brief mention has already been made of the mixed 
glands and of the various views regarding their possible signifi- 
eance. Hoyer (’90) described a mixed condition for some of the 
poison glands of the salamander. Lying between the unstained 
‘Riesenzellen’ of the granular gland, he found single cells or 
groups of cells which gave with thionin the specific color reaction 
for mucin. Mixed glands have been reported also by Heiden- 
hain (93a) and Nicoglu (’93). According to these investi- 
gators, this ‘Doppelbildung’ is a result of replacement of the 
poison gland by one of the mucous type. Nicoglu suggests that 
the replacement occurs as an adaptation, because the animal, 
through some unusual change in environment, has come to 
need more mucus than could be secreted by the normal mucous 
glands. Talke (’00) confirms the conclusions of Heidenhain 
and Nicoglu, and describes a ‘“‘Schleimsecernierendes Driisen- 
sickchen in dem Balge der alten Giftdriise.”’? The last three 
writers referred to deny the possibility of a direct metamorphosis 
of the slime cells into poison cells, as suggested by Hoyer (’90). 
Esterly (’04), in his work on the glands of Plethodon, describes 
small mucous sacs lying within the poison glands. He believes 
that, when the poison cells are exhausted, the mucous sac enlarges, 
replaces the poison gland, and very probably metamorphoses into 
a gland of the latter type. That is to say, the mucous cells may 
be directly differentiated into poison cells. Nordenskiéld (’05) 
has described a mixed condition in the toad ‘‘wo der Fundusteil 
der Driise von Schleimzellen, die tibrige Driise von Giftzellen 
ausgekleidet ist’ (p. 11). In another place, while discussing 
the relation of the two types of glands, he says: ‘‘Anderseits 
scheint jedoch in den meisten Fallen sehr friih eine bestimmte 
Sonderung der Funktion. einzutreten, so dass sich die junge 
Driise definitiv zur Schleimdriise oder Giftdriise ausbildet.” 
Nirenstein (’08), who worked on Salamandra maculosa and 
Triton, gives quite a different explanation of the small mucous 
sacs described within the lumina of the poison glands by Heiden- 
hain (’93 a), Nicoglu (’93), Talke (’00), and Esterly (04). 
